An exemplary embodiment of this application relates to an ink jet printer having a shuttling printhead that ejects droplets of either melted solid ink or liquid ink onto a moving recording medium or intermediate surface to print swaths of information that are perpendicular to the direction of movement thereof. More particularly, the exemplary embodiment relates to an ink jet printer having a two-dimensionally movable printhead that prints swaths of information on a recording medium or intermediate surface that moves at a constant velocity. The printed swaths of information are perpendicular to the moving direction of the recording medium or intermediate surface. A transfixing station may be located downstream from the printhead whereat the printed information on the intermediate surface may be transferred and fixed to a recording medium.
Droplet-on-demand ink jet printing systems eject ink droplets from printhead nozzles in response to pressure pulses generated within the printhead by either piezoelectric devices or thermal transducers, such as resistors. The ejected ink droplets are propelled to specific locations on a recording medium, commonly referred to as pixels, where each ink droplet forms a spot on the recording medium. The printheads contain ink in a plurality of channels, usually one channel for each nozzle, which interconnect an ink reservoir in the printhead with the nozzles.
In a thermal ink jet printing system, the pressure pulse is produced by applying an electrical current pulse to a resistor typically associated with each one of the channels. Each resistor is individually addressable to heat and momentarily vaporize the aqueous based ink in contact therewith. As a voltage pulse is applied across a selected resistor, a temporary vapor bubble grows and collapses in the associated channel, thereby displacing a quantity of ink from the channel, so that it bulges through the channel nozzle. The ink bulging through the nozzle is ejected from the nozzle as a droplet, during the bubble collapse on the resistor. The ejected droplet is then propelled to a recording medium. When the ink droplet hits the targeted pixel on the recording medium, the ink droplet forms a spot thereon. The channel from which the ink droplet was ejected is then refilled by capillary action, which, in turn, draws ink from an ink supply container.
In a typical piezoelectric ink jet printing system, the pressure pulses that eject liquid ink droplets are produced by applying an electric pulse to the piezoelectric devices, one of which is typically located within each one of the ink channels. Each piezoelectric device is individually addressable to cause it to bend or deform and pressurize the volume of liquid ink in contact therewith. As a voltage pulse is applied to a selected piezoelectric device, a quantity of ink is displaced from the ink channel and a droplet of ink is mechanically ejected from the nozzle associated with each piezoelectric device. Just as in thermal ink jet printing, the ejected droplet is propelled to a pixel target on a recording medium. The channel from which the ink droplet was ejected is refilled by capillary action from an ink supply. For an example of a piezoelectric ink jet printer, refer to U.S. Pat. No. 3,946,398.
The majority of color printers today use an aqueous ink in a thermal ink jet printer. If a shuttling printhead is used, the printhead is transported across a stationary recording medium, such as a sheet of paper, from one edge thereof to the opposite edge. This is usually referred to as the “X” or scan direction. Once the printhead has been transported in the X direction across the recording medium, either the recording medium or the printhead is advanced a distance of the height of a printed swath or a portion thereof in the direction perpendicular to the X direction usually referred to as the “Y” direction. The printhead is then scanned in the X direction back across the recording medium to the original edge thereof, so that another swath of information is printed. The subsequently printed swaths may be contiguous with the previously printed swaths or interlaced therewith. When the complete image is printed on the recording medium, it is removed and replaced with a clean recording medium and the process is repeated for a subsequent image.
An ink jet printhead can include one or more printhead die assemblies, each having a droplet ejecting portion and a channel portion. The channel portion includes an array of ink channels that bring ink into contact with the droplet ejectors, which are correspondingly arranged on the droplet ejecting portion. In addition, the droplet ejecting portion may also have integrated addressing electronics and driver transistors. The array of channels in a single die assembly is not sufficient to cover the full width of a page of recording medium, such as, for example, a standard sheet of paper. Therefore, a printhead having only one die assembly is scanned across the page of recording medium while the recording medium is held stationary and then the recording medium is advanced between scans. Alternatively, multiple die assemblies may be butted together to produce a full width printhead, such as, for example, the printhead disclosed in U.S. Pat. Nos. 4,829,324 and 5,221,397.
Because thermal ink jet printhead nozzles typically eject ink droplets that produce spots of a single size on the recording medium, high quality printing requires the ink channels and associated nozzles and corresponding printhead droplet ejectors to be fabricated at a high resolution, such as, for example, 600 per inch.
The ink jet printhead may be incorporated into a carriage type printer or a full width array type printer. The carriage type printer may have a printhead having a single die assembly or several die assemblies abutted together for a partial width size printhead. Since both single die and multiple-die, partial width printheads function substantially the same way in a carriage type printer, only the printer with a single die printhead will be discussed. The only difference, of course, is that the partial width size printhead will print a larger swath of information. The single die printhead, containing the ink channels and nozzles, can be connected to an ink supply attached thereto or located separately therefrom. The printhead is reciprocated to print one swath of information at a time, while the recording medium is held stationary. Each swath of information is equal to the height of the column of nozzles in the printhead. After a swath is printed, the recording medium is stepped a distance at most equal to the height of the printed swath, so that the next printed swath is contiguous or overlaps with the previously printed swath. When the subsequently printed swath is overlapped or partially overlapped with the previously printed swath, the printed spots or pixels may be interlaced to increase image resolution. This procedure is repeated until the entire image is printed. If the printhead is shuttled across the recording medium, the recording medium is held stationary until the complete image is printed. The printhead is scanned first in the X direction during which time it prints a swath of information and then is stepped in the Y direction without ejecting ink droplets prior to the next scan in the X direction.
In contrast, the page width printer includes a stationary printhead having a length sufficient to print across the width of sheet of recording medium. The recording medium is continually moved past the full width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. Another example of a full width array printer is described, for example, in U.S. Pat. No. 5,192,959.
Ink jet printing systems typically eject ink droplets based on information received from an information output device, such as, a personal computer. Typically, this received information is in the form of a raster, such as, for example, a full page bitmap or in the form of an image written in a page description language. The raster includes a series of scan lines comprising bits representing individual information elements or pixels. Each scan line contains information sufficient to eject a single line of ink droplets across the recording medium in a linear fashion from one nozzle. For example, ink jet printers can print bitmap information as received or can print an image written in the page description language once it is converted to a bitmap of pixel information.
The problem of ink drying time and paper cockling are widely recognized issues when printing high coverage areas with aqueous based inks, particularly when printing color images. The problem of drying time and paper cockling is substantially reduced when solid ink is used and the printhead ejects droplets of melted ink onto the recording medium, where the melted ink droplets solidify immediately. Further improvement in the drying time and cockling problem is obtained when the printhead ejects droplets of melted ink onto an intermediate surface, such as, for example, a drum, that has a release agent coating thereon. Once the image is fully formed on the intermediate surface, the image is then transferred to a recording medium, such as paper. The transfer is generally conducted in a nip formed by the rotating intermediate belt or drum surface and a rotatable heated pressure roll. As a sheet of paper is transported through the nip, the fully formed image is transferred from the intermediate belt or drum surface to the sheet of paper and concurrently fixed thereon. This transfer technique of using the combination of heat and pressure at a nip to transfer and fix the image to a recording medium passing through the nip is usually referred to as “transfixing,” a well known technology.
In all of the above mentioned current ink jet printers, there is a loss of efficiency induced by time spent during which the printhead does not eject ink droplets. In a shuttle printhead architecture, this time is spent while decelerating and accelerating the printhead as it turns around between scans. In the intermediate drum configuration, this time is spent as the printhead passes over inter image spaces or dead bands, and also during the time that transfixing occurs. To minimize this unused time, reduction in the time spent transfixing has been the goal, but transfixing speeds of 25 inches per second or higher has been found not to produce prints with an appropriate level of print quality and durability. One solution is to use a separate off line transfixing step, but this results in added costs, complexity and reliability issues for the printer system. In addition to the transfixing time, the intermediate drum surface must be re-coated with a release agent between prints, resulting in further time being spent while the printhead is not printing. In current ink jet printers using intermediate transfer members, the transfixing process must be performed serially after the imaging process. As printer speeds increase, the time required for the transfixing process must get shorter, forcing the transfixing process to higher speeds, causing degraded image quality.
U.S. Pat. No. 5,099,256 discloses a thermal ink jet printer having a translatable multicolor printhead and a rotatable intermediate drum with a film forming silicone polymer layer on the outer surface thereof. The drum surface is heated to dehydrate the aqueous based ink droplets deposited thereon from the printhead at a first location. The drum is rotated and the dehydrated droplets are transferred from the drum to a recording medium at a transfer station positioned adjacent the drum at a second location.
U.S. Pat. No. 6,033,053 discloses an ink jet printing cartridge in the form of a cylindrical drum having a plurality of individual printheads helically formed on and covering the outer surface of the drum. The drum is rotated about its axis, and as the drum is rotated, the printheads confronting a sheet of paper are actuated to eject ink droplets, while the sheet of paper is moved past the rotating drum shaped cartridge.
U.S. Pat. No. 6,394,577 discloses an ink jet printing apparatus for forming an ink image on a receiver or recording medium that is attached to the surface of a rotatable drum. The drum is rotated about its axis, and the printing apparatus has an ink jet printhead that is movable in a direction parallel to the drum axis and ejects ink droplets onto the receiver while the drum is rotated at a predetermined velocity. The printing apparatus moves the printhead at a velocity less than that of the drum, so that the printhead scans an area of the drum surface that is skewed relative to the drum surface. Control circuitry simultaneously controls the movement of the drum and printhead and actuates the printhead to form an ink image within the skewed scans, but only within the boundaries of the receiver.
U.S. Pat. No. 6,511,172 discloses an ink jet printing apparatus having a flat transport belt for transporting a printing sheet to a region opposite the ejection openings of the printheads. An electrostatic generating means provides an electrostatic suction or attraction force on the surface of the transport belt. A control means generates the attraction force only in a region opposite the printheads.
U.S. Pat. No. 6,588,877 discloses a bi-directional envelope printing system having a reciprocating carriage that moves from a maintenance station in a first direction across a printing location to an end position. The carriage then returns across the printing location to the maintenance station. The carriage includes multiple ink jet printheads, each printing a swath of information that has a specific swath height. The printheads print on a first envelope while traveling in the first direction, and the printheads print on a second envelope on the return trip to the maintenance station. An envelope transport delivers each envelope to the printing location and removes the printed envelope prior to delivery of the subsequent envelope to be printed.